혼합물 2 Mg + Co 의 수소 저장 특성에 관한 연구

송명엽 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.10

Among many metals the magnesium has excellent hydrogen-storage characteristics except that its hydriding and dehydriding rates are low Many works have been carried but in order to improve the reaction rates of magnesium with hydrogen. But their processes for the sample preparation were energy-consuming and complicated. In this work, to simplify the process of sample preparation, magnesium powder and cobalt powder were mixed in a 2 : 1 atomic ratio and pressed under 5 kbar to cylindrical pellet. The activation of the mixture was completed after about 15 hydriding-dehydriding cycles at about 700K and 25 barH₂The activated mixture absorbed hydrogen of about 2.8 weight percent at about 700K and 25 barH₂. The hydrogen storage capacity did not change until the 50th hydriding-dehydriding cycle. Equilibrium plateau pressures appeared at two different pressures, for example at 698K, 9 bar and about 14.5 bar. Under hydrogen pressures of relatively small deviations from the equilibrium plateau pressure, the hydriding reaction rates were controlled by the nucleation. After nucleation they were controlled by Knudsen flow and ordinary gaseous diffusion. Dehydriding reaction rates were controlled by the transformation of hydide into hydrogen and α-solid solution of Mg and Co.

Effects of Zn(BH4)2, Ni, and/or Ti Doping on the Hydrogen-Storage Features of MgH2

송명엽,곽영준 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.3

In the present work, MgH2 was doped with Zn(BH4)2, Ni, and/or Ti to improve its hydrogen absorption and release features. Samples were prepared by grinding in a planetary ball mill in a hydrogen atmosphere. To increase the hydrogen absorption and release rates without significantly sacrificing hydrogenstorage capacity the additive percentages were less than 10 wt%. The activation of these samples was not necessary. M2.5Z2.5N had the largest quantity of hydrogen absorbed in 60 min, Qa (60 min), at the number of cycles, NC, of one (NC=1), followed in descending order by M5Z2.5N2.5T and M1Z. M5Z2.5N2.5T had the highest initial release rate, followed in descending order by M2.5Z2.5N and M1Z. M5Z2.5N2.5T had the highest initial release rate and M1Z had the largest quantity of hydrogen released in 60 min, Qd (60 min) at NC=2. The sample without Ni (M1Z) had the lowest initial release rate at NC=2. Among these samples, M2.5Z2.5N had the best hydrogen absorption and release properties. Grinding MgH2 with Zn(BH4)2, Ni, and/ or Ti in hydrogen is believed to create defects, induce lattice strain, generate cracks, and reduce the particle sizes. The formed hydrides β-MgH2, γ-MgH2, and TiH1.924 are believed to help produce finer particles in the sample by being pulverized during grinding in hydrogen. The formed Zn and TiH1.924 and the NaCl remained unreacted during cycling. It was deemed that the formed Mg2Ni phase contributed to the increases in the initial hydrogen absorption and release rates and the improvement in cycling performance by absorbing and releasing hydrogen itself.

Hydrogen Storage Properties of Mg Alloy Prepared by Incorporating Polyvinylidene Fluoride via Reactive Milling

송명엽,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.12

In the present work, we selected a polymer, polyvinylidene fluoride (PVDF), as an additive to improve the hydrogenation and dehydrogenation properties of Mg. 95 wt% Mg + 5 wt% PVDF (designated Mg-5PVDF) samples were prepared via milling in hydrogen atmosphere (reactive milling), and the hydrogenation and dehydrogenation characteristics of the prepared samples were compared with those of Mg milled in hydrogen atmosphere. The dehydrogenation of magnesium hydride formed in the as-prepared Mg- 5PVDF during reactive milling began at 681 K. In the fourth cycle (n=4), the initial hydrogenation rate was 0.75 wt% H/min and the quantity of hydrogen absorbed for 60 min, Ha (60 min), was 3.57 wt% H at 573 K and in 12 bar H2. It is believed that after reactive milling the PVDF became amorphous. The milling of Mg with the PVDF in hydrogen atmosphere is believed to have produced defects and cracks. The fabrication of defects is thought to ease nucleation. The fabrication of cracks is thought to expose fresh surfaces, resulting in an increase in the reactivity of the particles with hydrogen and a decrease in the diffusion distances of hydrogen atoms. As far as we know, this investigation is the first in which a polymer PVDF was added to Mg by reactive milling to improve the hydrogenation and dehydrogenation characteristics of Mg.

Raising the Dehydrogenation Rate of a Mg-CMC (Carboxymethylcellulose, Sodium Salt) Composite by Alloying Ni via Hydride-Forming Milling

송명엽,최은호,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C6H7O2(OH)x(C2H2O3Na)y]n) (named Mg-5 wt%CMC) were prepared through hydride-forming milling. Mg-5 wt%CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg-5 wt%CMC. In this study, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 wt% Ni (named Mg-5 wt%CMC-5 wt%Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg-5 wt%CMC-5 wt%Ni was completed at the 3rd hydrogenation-dehydrogenation cycle (N=3). Mg-5 wt%CMC-5 wt%Ni had an effective hydrogen-storage capacity (the quantity of hydrogen stored for 60 min) of 5.83 wt% at 593 K in 12 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni dehydrogenated at N=4 contained Mg and small amounts of MgO, β-MgH2, Mg2Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg2Ni formed during hydrogenation-dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg-5 wt%CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg.

Hydrogen Uptake and Release Characteristics of Mg-xTaF5-xVCl3 (x=1.25, 2.5, and 5)

송명엽,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8

TaF5 and VCl3 were chosen as additives to enhance the hydrogen uptake and release rates of Mg. The total content of the additives was not more than 10 wt% since too high content reduces the fraction of Mg and thus the hydrogen storage capacity of the alloys. Samples with compositions of Mg-x wt% TaF5-x wt% VCl3 (x=1.25, 2.5, and 5) were prepared by reactive mechanical grinding. The temperatures at which the asmilled Mg-xTaF5-xVCl3 (x=1.25, 2.5, and 5) began to release hydrogen quite rapidly were 538, 613, and 642 K, respectively. Activation of the samples was not needed. In the first cycle (n=1), Mg-2.5TaF5-2.5VCl3 had quite a high effective hydrogen storage capacity (the amount of hydrogen absorbed for 60 min) of 5.86 wt%. Among the three samples, Mg-1.25TaF5-1.25VCl3 had the best hydrogen release properties. In n=4, Mg-1.25TaF5- 1.25VCl3 had the largest quantity of hydrogen released for 60 min at 593 K in 1.0 bar H2, releasing 0.23 wt% H for 5 min, 0.34 wt% H for 10 min, and 3.31 wt% H for 60 min. After hydrogen uptake-release cycling, Mg- 1.25TaF5-1.25VCl3 had the smallest particle size. In n=5, Mg-1.25TaF5-1.25VCl3 released 2.01 wt% H for 5 min, 3.78 wt% H for 10 min, and 4.89 wt% H for 60 min at 623 K in 1.0 bar H2.

Development of a Mg-Based Alloy with a Hydrogen-Storage Capacity of 7 wt% by Adding a Polymer CMC via Transformation-Involving Milling

송명엽,최은호,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.5

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydriding and dehydriding properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may put the milled samples in good states to absorb and release hydrogen rapidly. Samples with compositions of 95 wt% Mg + 5 wt% CMC (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (named Mg-10CMC) were made using transformation-involving milling. Mg-5CMC was activated in about 3 hydriding-dehydriding cycles. After activation, Mg-5CMC had a larger amount of hydrogen absorbed in 60 min, Ha (60 min), than Mg-10CMC and milled Mg. At the fourth cycle (CN=4), Mg-5CMC had a very high beginning hydriding rate (1.45 wt% H/min) and Ha (60 min) (7.38 wt% H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.4 wt% at 593 K in hydrogen of 12 bar at CN=4. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of β- MgH2 and MgO, and Mg-5CMC dehydrogenated at 593 K in hydrogen of 1.0 bar at the 4th cycle contained Mg and tiny amounts of β-MgH2 and MgO, with no evidence of the phases related to CMC. The milling of Mg with CMC in hydrogen is believed to introduce defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydriding and dehydriding properties of Mg.

Amelioration of the hydriding and dehydriding kinetics of Mg by reactive mechanical grinding with Ni and Fe2O3 purchased and prepared by spray conversion

송명엽,SungHwan Baek,박혜령,홍성현 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.5

The activated 76.5 wt%Mg–23.5 wt%Ni (Mg–Ni) has a lower hydriding rate, compared with Mg–23.5 wt%Ni heat-treated after melt spinning, due to the nonhomogeneous distribution of Ni particles in the mixture and the larger sizes of the particles. Among 76.5 wt%Mg–23.5 wt%Ni (Mg–Ni), 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe2O3 (Mg–Ni–O), and 71.5 wt%Mg–23.5 wt%Ni–5 wt% Fe2O3(spray conversion) (Mg–Ni–Osc) samples, Mg–Ni–Osc has the highest hydriding and dehydriding rates. The reactive mechanical grinding of Mg with Ni, purchased Fe2O3 or Fe2O3(spray conversion) is considered to facilitate nucleation and shorten diffusion distances of hydrogen atoms. After hydriding–dehydriding cycling, all the samples contain Mg2Ni phase. The samples with Fe2O3 and Fe2O3(spray conversion) as starting materials contain Mg(OH)2 phase after hydriding–dehydriding cycling as well as after reactive mechanical grinding. 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Hydrogen storage properties of pure Mg

송명엽,곽영준,이성호,박혜령 대한금속·재료학회 2014 대한금속·재료학회지 Vol.52 No.4

The hydrogen storage properties of pure Mg are investigated at 573 K under 12 bar H2. In addition,in order to increase the hydriding and dehydriding rates of pure Mg, it is ground under hydrogen (reactivemechanical grinding, RMG), and its hydrogen storage properties are investigated. The pure Mg absorbshydrogen very slowly. At n = 1, the pure Mg absorbs 0.05 wt.% H for 5 min, 0.08 wt.% H for 10 min, and0.29 wt.% H for 60 min at 573 K under 12 bar H2. The hydriding rate decreases as the number of cyclesincreases from n = 7. At n = 7, the pure Mg absorbs 0.96 wt.% H for 5 min, 1.29 wt.% H for 10 min, and2.20 wt.% H for 60 min. At n = 1, the pure Mg after RMG does not absorb hydrogen. The hydriding rate of pureMg after RMG increases as the number of cycles increases from n = 1 to n = 11. The pure Mg after RMGabsorbs 1.91 wt.% H for 5 min, 2.61 wt.% H for 10 min, and 3.65 wt.% H for 60 min at n = 11. The reactivemechanical grinding of the pure Mg and the hydriding-dehydriding cycling of the pure Mg after RMG arebelieved to create defects on the surface and in the interior of Mg particles and to form cracks in Mgparticles.

Development of MgH_2-Ni Hydrogen Storage Alloy Requiring No Activation Process via Reactive Mechanical Grinding

송명엽,곽영준,Seong Ho Lee,박혜령 대한금속·재료학회 2012 대한금속·재료학회지 Vol.50 No.12

MgH_2 was employed as a starting material instead of Mg in this work. A sample with a composition of 94 wt% MgH_2-6 wt% Ni (called MgH_2-6Ni) was prepared by reactive mechanical grinding. The hydriding and dehydriding properties were then examined. An MgH_2-Ni hydrogen storage alloy that does not require an activation process was developed. The alloy was prepared in a planetary ball mill by grinding for 4 h at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.74 wt%H for 5 min, 4.07 wt% H for 10 min, and 4.41 wt% H for 60 min at 573 K under 12 bar H_2, and desorbed 0.93 wt% H for 10 min, 1.99 wt% H for 30 min, and 3.16 wt% H for 60 min at 573 K under 1.0 bar H_2. MgH_2-6Ni after reactive mechanical grinding contained β-MgH_2 (a room temperature form of MgH_2), Ni,γ-MgH_2 (a high pressure form of MgH_2), and a very small amount of MgO. Reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation, and to reduce the particle size of Mg. Mg_2Ni formed during reactive mechanical grinding also increases the hydriding and dehydriding rates of the sample.

수소 분위기에서 Mg와 VCl3의 밀링에 의한 Mg의 수소 흡수 방출 특성의 향상

송명엽,이성호,곽영준 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.10

VCl3 (vanadium (III) chloride) was selected as an additive to Mg to increase the hydrogenation and dehydrogenation rates and the hydrogen storage capacity of Mg. Instead of MgH2, Mg was used as a starting material since Mg is cheaper than MgH2. Samples with a composition of 95 wt% Mg + 5 wt% VCl3 (named Mg-5VCl3) were prepared by milling in hydrogen atmosphere (reactive milling). In the first cycle (n=1), Mg- 5VCl3 absorbed 5.38 wt% H for 5 min and 5.95 wt% H for 60 min at 573 K in 12 bar hydrogen. The activation of Mg-5VCl3 was completed after three hydrogenation-dehydrogenation cycles. During milling in hydrogen, β-MgH2 and γ-MgH2 were produced. The formed β-MgH2 and γ-MgH2 are considered to have made the effects of reactive milling stronger as β-MgH2 and γ-MgH2 themselves were being pulverized. The introduced defects and the interfaces between the Mg and the phases formed during the reactive milling and during hydrogenation-dehydrogenation cycling are believed to serve as heterogeneous active nucleation sites for MgH2 and Mg-H solid solution. The phases generated during hydrogenation-dehydrognation cycling are also believed to prevent the particles from coalescing during hydrogenation-dehydrognation cycling.